Disk drives are information storage devices that use magnetic media to store data. Referring to FIG. 1a, a typical disk drive in related art has a magnetic disk and a drive arm to drive a head gimbal assembly 277 (HGA) (the HGA 277 has a suspension (not labeled) with a slider 203 mounted thereon). The disk is mounted on a spindle motor which causes the disk to spin and a voice-coil motor (VCM) is provided for controlling the motion of the drive arm and thus controlling the slider 203 to move from track to track across the surface of the disk to read data from or write data to the disk.
However, because of the inherent tolerance resulting from VCM and the suspension that exists in the displacement (off track) of the slider 203, the slider 203 can not attain a quick and fine position control which will affect the slider 203 to read data from and write data to the magnetic disk.
To solve the above-mentioned problem, piezoelectric (PZT) micro-actuators are now utilized to modify the displacement of the slider 203. That is, the PZT micro-actuator corrects the displacement of the slider 203 on a much smaller scale, and also compensates for the resonance tolerance of the VCM and the suspension. It enables a smaller recording track width, increases the ‘tracks per inch’ (TPI) value by 50% of the disk drive unit and also can reduce the head seeking and settling time (it is equivalent to increase the surface recording density).
Referring to FIG. 1b, a traditional PZT micro-actuator 205 comprises a ceramic U-shaped frame 297 which comprises two ceramic beams 207 with two PZT pieces (not labeled) on each side thereof. With reference to FIGS. 1a and 1b, the PZT micro-actuator 205 is physically coupled to a suspension 213, and there are three electrical connection balls 209 (gold ball bonding or solder ball bonding, GBB or SBB) to couple the micro-actuator 205 to the suspension traces 210 in each one side of the ceramic beam 207. In addition, there are four metal balls 208 (GBB or SBB) to couple the slider 203 to the suspension traces 210 for electrical connection. FIG. 1c shows a detailed process of inserting the slider 203 into the micro-actuator 205. The slider 203 is bonded with the two ceramic beams 207 at two points 206 by epoxy dots 212 so as to make the motion of the slider 203 dependent of the ceramic beams 207 of the micro-actuator 205.
When power supply is applied through the suspension traces 210, the PZT pieces of the micro-actuator 205 will expand or contract to cause the two ceramic beams 207 of the U-shaped frame 297 deform and then make the slider 203 move on the track of the disk. Thus a fine head position adjustment can be attained.
However, because the PZT micro-actuator 205 are mounted on the suspension tongue (not labeled), when the PZT micro-actuator 205 is excited, it will only do a translational motion to sway the slider 203 above the disk, the sway movement will generate a reaction force exerted to the suspension tongue so as to cause a suspension vibration resonance which has a same resonance as shaking the suspension base plate. This will affect the dynamic performance of the HGA and limit the servo bandwidth and the storage capacity improvement of HDD (hard disk drive). As shown in FIG. 2, numeral 201 represents a resonance curve when shaking the suspension base plate and numeral 202 represents a resonance curve when exciting the micro-actuator 205. Under a frequency of 20K, there are a lot of gain peaks of suspension frequency response in plus side and minus side, which indicate a bad characteristic of resonance. The figure clearly shows the above-mentioned problem.
Hence, it is desired to provide a micro-actuator unit, head gimbal assembly, disk drive to solve the above-mentioned problems.